1. Technical Field of the Invention
The present invention describes a room temperature-curable organopolysiloxane composition. More specifically, the present invention describes a room temperature-curable organopolysiloxane composition wherein the surface of the silicone rubber, after curing at room temperature, is readily painted.
2. Prior Art Technologies and Their Drawbacks
It is known in the prior art that the entire composition is cured into a rubbery elastomer at room temperature by the reaction of a hydroxyl-terminated organopolysiloxane with an amide group-containing organosilicon compound or an aminoxy group-containing organosilicon compound as the curing agent. Such compositions can also employ bifunctional compounds and polyfunctional compounds with .gtoreq.3 functional groups as the curing agent. Their ratios are varied in order to vary the properties over a broad range from low modulus-high ductility to high modulus-low ductility. In particular, a low modulus-high ductility composition is used as a construction sealing material because organopolysiloxanes exhibit excellent weather resistance and fatigue resistance.
However, silicone sealing materials suffer the significant drawback that the surface of the cured silicone rubber either cannot be painted or is painted with difficulty because the paint will not coat or will not adhere (this definition applies below). Due to this drawback, limitations are imposed on the applications of silicone sealing materials although they exhibit excellent properties.
Various methods were examined by the present inventors in order to improve upon this drawback to the paintability of silicone sealing materials. A method was proposed by Fukayama in U.S. Pat. No. 4,447,576, issued May 8, 1984, in which an organopolysiloxane composition curing by displacement of aminoxy or amido groups is combined with an alcohol containing a specific functional group.
However, the above method is generally executed in a 3-package configuration. In particular, because the alcohol containing a specific functional group and comprising the third component is present in extremely small quantities, the paintability and physical properties will vary significantly due to errors in blending at the time of use or due to small differences in the quantity remaining in the container after addition. In addition, the composition to which the prescribed quantity of the third component has, in fact, been added results in nonuniform product and presents the drawback that the individual parts of the molding have an inhomogeneous paintability or inhomogeneous physical properties.
On the other hand, when the quantity of said alcohol containing a specific functional group is increased in order to increase the paintability, the properties of the composition are degraded because the interior of the composition exhibits poor curability. For this reason, the prior art compositions have the drawback of an incompatibility between the desired paintability and the desired physical properties.
3. Goal of the Invention
The goal of the present invention is to eliminate the above-mentioned drawbacks by providing an organopolysiloxane composition which is paintable after curing at room temperature.